Probing benzene in a new way: High-resolution time-resolved rotational spectroscopy

Precise values for the rotational constants of benzene in both the ground a nd the electronically excited state have been obtained by time-resolved rot ational spectroscopy. A relative uncertainty on the order of 10(-5) for the se constants has been achieved, while the. absolute values are in excellent agreement with data from rotationally resolved optical spectroscopy. Thus benzene serves as a molecular benchmark for high-resolution rotational cohe rence spectroscopy (RCS) with the perspective that the influence of vibrati ons on the equilibrium structure could be studied for a medium-sized molecu le by this method soon.